CANNABIS USE DOUBLES INCIDENCE OF PSYCHOSIS

Young people who smoke cannabis or marijuana for six years or more are
twice as likely to have psychotic episodes, hallucinations or
delusions than people who have never used the drug, scientists said on
Monday.

The findings adds weight to previous research which linked psychosis
with the drug and will feed the debate about the level of controls
over its use.

Despite laws against it, up to 190 million people around the world use
cannabis, according to United Nations estimates, equating to about
four per cent of the adult population.

John McGrath of the Queensland Brain Institute in Australia studied
more than 3,801 men and women born between 1981 and 1984 and followed
them up after 21 years to ask about their cannabis use and assessed
them for psychotic episodes.

"Compared with those who had never used cannabis, young adults who had
six or more years since first use of cannabis were twice as likely to
develop a non-affective psychosis," McGrath wrote in a study published
in the Archives of General Psychiatry journal. They were also four
times as likely to have high scores in clinical tests of delusion. A
"dose-response" relationship showed the longer the duration since
first cannabis use, the higher the risk of psychosis-related symptoms.

McGrath said, however, that "the nature of the relationship between
psychosis and cannabis use is by no means simple" and more research
was needed to examine the mechanisms at work.